Articles
ARE HRP GENES OF ERWINIA AMYLOVORA INVOLVED IN EARLY SUPPRESSION OF HOST DEFENCE MECHANISMS?
The protective ability of 32 avirulent insertion mutants of E. amylovora was investigated.
Young apple seedlings were inoculated after wounding of the youngest leaf: in "sequenced inoculations" the avirulent mutant was applied 2 h before the virulent strain; in "co-inoculations" the two strains were mixed just before applying to the wound.
In sequenced inoculation experiments, most mutants were consistently able to protect apple seedings from infection.
In co-inoculation experiments, 6 mutants only exhibited a significant protective ability which appeared to be specifically linked to the alteration of some hrp genes.
Thus, a rapid protective effect, only revealed through the co-inoculation procedure, might be induced following the inactivation of these hrp genes.
The protective effect was modulated by the avirulent/virulent ratio, and a minimal inoculum level of the avirulent mutant concentration appeared to be necessary to induce a significant level of protection.
This suggested that protection might occur through an early competition between avirulent and virulent strains for putative infection sites.
Moreover, population dynamics studies indicated that the protective effect might involve a plant defence response.
Assuming that the alteration of given hrp genes induces a rapid protective effect connected with a plant defence response, the question is then raised of the role these genes in the pathogenic strain.
It might be suggested that, in a successful infection process, they are involved in the early suppression of host defence mechanisms.